Development of hybrid plant breeding has made possible considerable advances in quality and quantity of crops produced. Increased yield and combination of desirable characteristics, such as resistance to disease and insects, heat and drought tolerance, along with variations in plant composition are all possible because of hybridization procedures. These procedures frequently rely heavily on providing for a male parent contributing pollen to a female parent to produce the resulting hybrid.
Field crops are bred through techniques that take advantage of the plant's method of pollination. A plant is self-pollinated if pollen from one flower is transferred to the same or another flower of the same plant or a genetically identical plant. A plant is cross-pollinated if the pollen comes from a flower on a genetically different plant.
In certain species, such as Brassica campestris, the plant is normally self-sterile and can only be cross-pollinated. In predominantly self-pollinating species, such as soybeans, wheat, and cotton, the male and female plants are anatomically juxtaposed such that during natural pollination, the male reproductive organs of a given flower pollinate the female reproductive organs of the same flower.
Bread wheat (Triticum aestivum) is a hexaploid plant having three pairs of homologous chromosomes defining genomes A, B and D. The endosperm of wheat grain comprises two haploid complements from a maternal cell and one from a paternal cell. The embryo of wheat grain comprises one haploid complement from each of the maternal and paternal cells. Hexaploidy has been considered a significant obstacle in researching and developing useful variants of wheat. In fact, very little is known regarding how homologous genes of wheat interact, how their expression is regulated, and how the different proteins produced by homologous genes function separately or in concert. Strategies for manipulation of expression of male-fertility polynucleotides in wheat will require consideration of the ploidy level of the individual wheat variety. Triticum aestivum is a hexaploid containing three genomes designated A, B, and D (N=21); each genome comprises seven pairs of nonhomologous chromosomes. Einkorn wheat varieties are diploids (N=7) and emmer wheat varieties are tetraploids (N=14).
An essential aspect of much of the work underway with genetic male sterility systems is the identification of genes influencing male fertility. Such a gene can be used in a variety of systems to control male fertility including those described herein.